A rather vaulable Irish manuscript produced ca. 1150. There was an earlier Book of Leinster, called the Book of Glendalough, and an even earlier Book of Leinster, which is now lost. The confusion between the two different surviving manuscripts has continued to the present day, with the Oxford Dictionary of Celtic Mythology identifying one with the other, while the diplomatic edition distinguishes between the two. Based upon its earlier name of Lebhar Na Núachongbála, it is believed that it was produced at a monestary called Nevin, of which there were about six at this time. This has later been identified with Noughaval, near the town of Stradbally, Co. Waterford.

At any rate it made its way to Trinity College in this manner:

"It was one of a score or more of Irish manuscripts purchased during a tour in Ireland in 1700 by the Welsh archaeologist Edward Lhwyd, and purchased after his death in 1709 by Sir Thomas Sebright, and presented to the College by Sir John Sebright, the sixth baronet, in 1786."[1]

In 1954, a five volume diplomatic edition, edited by R. I. Best, Osborn Bergin, and M. A. O'Brien, was published by the Dublin Institute for Advanced Studies. The sixth volume was not completed until 1983, by Anne O'Sullivan, as the original editors had died before completing the work.